This happened about 2hours ago.

Backgroud: I was making dinner, "tunaslaw" with pasta, and we sat down to eat. Just 30 min earlier her mom brought her flowers since she doesn't have a bf and yesterday her plans failed with her friends (they were supposed to come over)

After dinner she wanted help with cutting the root of the flowers and then put them in water.

Me as a considerate stand in dad offered to help if she brought me the flowers and a knife.

Flowers in hand, waiting for the knife.. She comes forward with the knife and stabs me in the hand when I reach to recieve it.

My response was this: Ouch! What did you do? Her and her mom: surprised pikachu face Me: (Fairly calm voice) don't you know how to hand someone a knife?

That was mistake nr1, I didn't ask politely enough.

Completely ignoring she moves along to wash her hands (which she always do after dinner). Her mother tells me how I was in the wrong reaching for the knife she was supposed to give me.

I was trying to tell the daughter how to give someone a sharp object but I was met with eye rolling and the comment "well I don't know, I don't care" and the mother (my gf) even told me it was my fault since I reached for it and she was supposed to put it on the table.

I then told my gf I felt like I was not in the wrong trying to tell my stepdaughter how to handle sharp objects and the response was the following:

You should have been more calm and not ask "don't you know how to handle sharp objects?"

Which eventually led to my gf yelling at me and now there's a lot of negative energy in our house.

TL;DR I got stabbed and apparently wasn't allowed to show emotions which led to the point I'm the bad guy